1. Field of the Invention
The present invention relates to water-dispersible alumina and, more particularly, to a method for producing an alpha-alumina monohydrate having enhanced water dispersibility.
2. Description of the Prior Art
As is well known, alpha-alumina monohydrate has widespread commercial usage in such applications as abrasives, frictionizing paper surfaces, fiberglass surfaces, and metal surfaces; as static and soil protection agents on wool, nylon, and acrylic carpets; and as dispersing agents in rug shampoos, etc. In such commercial usages, the alumina is typically utilized as a dispersion in an aqueous acidic solution. It has long been known that adding acid to an aqueous alumina slurry that is dried to produce alpha-alumina monohydrate results in a product that is dispersible in water to a high degree. Indeed, in U.S. Pat. No. 4,676,928, incorporated herein by reference for all purposes, there is disclosed a method for enhancing the dispersibility of alumina in an acid solution by aging an alumina slurry containing a monobasic acid at elevated temperatures, e.g., at a temperature above about 70.degree. C. for a period of time sufficient to convert the greater portion of the alumina to a colloidal sol. The advantage of the process disclosed in U.S. Pat. No. 4,676,928 is that it produces an alumina having enhanced water dispersibility but with a generally lower acid content, thus avoiding the problems of corrosiveness and handling inherent in alumina compositions with high acid contents. However, the method still produces an acidic product and, moreover, requires extended aging at elevated temperatures.
U.S. Pat. No. 4,055,509, incorporated herein by reference for all purposes, discloses a process for increasing or enhancing the water dispersibility of alpha-alumina monohydrate by dry mixing alpha-alumina monohydrate with an effective amount of a salt compound, such as, for example, a salt having the formula MX wherein M is a polyvalent metal cation constituent for which the solubility product K.sub.SP of the corresponding metal hydroxide is less than 10.sup.-20 and wherein X is an anion constituent derived from a monovalent acid having an ionization constant K.sub.A greater than 10.sup.+1.